1. Field of the Invention
The present invention relates to a method for fabricating LED (Light Emitting Diode), and more particularly to a method using sedimentation to add the phosphor onto the surface of the LED, so as to allow the phosphor to absorb the light from the illumination chip and emit a light having the wave length that is different from that of the absorbed light. The emitted light from the phosphor combines with the light from the illumination chip to form a become a desired visible light, such as white, red, green light . . . etc.
2. Prior Art Description
Because LED is light-weight, energy saving and durable, it becomes more and more popular around the world. Especially, the LED is taking place of the normal fluorescent light in daily use. However, the manufacturer uses the LED's characteristic of emitting a mono-color in its peak and places a red, a blue and a green illumination chips or the a yellow and a blue chips side by side. Thereafter, by controlling the current and voltage, the illumination chips are able to emit a desired white light. Although, this kind of arrangement does have the effect to generate the desired white light, the mixing of different lights often causes color spot, which causes an inclination of a certain color to the emitted light.
To cope with the problem, with reference to FIGS. 9 and 10, a method for fabricating the LED is developed and comprises the steps of:
Fixing the chip (81): an illumination chip (93) is adhered to a bracket (91) by means of a conductive gel; PA1 Wire bonding (82): a pair of wires (96) is welded between the chip (93) and the bracket (91); PA1 Mixing (83): a phosphor (941) is mixed with a silica gel to become an adhesive (94); PA1 Gluing (84): the adhesive (94) is glued on the outer face of the chip (93); PA1 Forming (85): a casing (95) made of epoxy is used to encase the chip (93) and the bracket (91) to form a LED (9); and PA1 Testing (86): tests are held to examine the spectrum of the formed LED. PA1 1. The method requires that the chip and the wires should be first fixed and that the adhesive (94) should also be pre-mixed to have the desired concentration, which is quite complex and is cost ineffective; PA1 2. Because the adhesive (94) is glued on the outer face of the chip (93), the thickness of the glued adhesive (94) and the concentration of the adhesive will affect the quantity of the phosphor contained in the adhesive (94) and this will eventually affect the characteristic of the emitted light; PA1 3. The adhesive on the outer surface of the chip (93) will be heated after applied so as to form the casing (95) required for the chip (93), which is too time consuming and the quality and quantity of the production can not be well controlled; PA1 4. Due to the fraction coefficient of the adhesive (94) and the casing (95) being different, the emitted light from the chip (93) will be affected; PA1 5. Should the phosphor (941) be spread on the outer face of the chip (93), i.e. on the casing (95), the phosphor (941) is quite easy to come off from the casing (95) by any kind of impact or scratch and the two different wavelength lights can't reach the even mixing effect. Thus, it is will only see blue light in some part of spatial light output pattern. PA1 6. The ultraviolet rays from the sun light will easily increase the temperature of the casing (95), which will increase the aging to the casing (95) and will have an unwanted effect to the emitted light.
The method uses the chip (93) to emit the blue light and the phosphor absorbs a part of the emitted blue light and then emits a yellow light to mix with the blue light to become white light.
This method does have the effect to generate the white light, however it till encounters drawbacks, such as:
To overcome the above mentioned shortcomings, the present invention provides an improved method for fabricating the light emitting diode.